280 PHILOSOPHICAL TRANSACTIONS. [aNNO 1787. 



lowing proportions were used: the temperature of the air being 65°, to water 



4 oz., at 63", were added, 



Of sal ammoniac 3 xi thermometer sunk to 32°, that is, 31° 



Of nitre 3 x 24°, that is, 8° 



Of Glauber's salts § ij 17°, that is, 7° 



46° 



In this way he froze water on a day so hot that the thermometer in the shade 

 stood at 70°. By first cooling the salts and water in one mixture, and then 

 making another of these cooled materials, he sunk the thermometer 64°. 



A^ugust 28. The temperature of the air being 65°, 4- an oz. of rectified 

 spirit of wine was diluted with 3^ oz. of water, and immersed in the same fri- 

 gorific mixture. When cooled to 24°, it began to freeze. A quantity of the 

 the neutral salts, likewise cooled in the mixture, were put into the diluted 

 spirit, when the thermometer fell to — 4°, so that the liquor was cooled 

 69 degrees. Spirit of nitre, diluted in the manner described by Mr. Cavendish 

 (Phil. Trans., vol. 7^), having reduced the thermometer to — 3°, sal ammo- 

 niac was added, on which it fell to — 1 5°. Nitrated volatile alkali, during its 

 solution in water, reduced the thermometer to 35° (from 50° to 15°); but the 

 cold was not increased by sal ammoniac or nitre. 



Mr. Walker's most remarkable experiment was made on the 21st of March, 

 1787, when he found that nitrous acid, when poured on Glauber's salt, pro- 

 duced effects nearly the same as when it is poured on pounded ice ; and that the 

 cold thus produced, is rendered still more intense by the addition of sal ammo- 

 niac in powder. Mr. Walker, by many trials, discovered that the best propor- 

 tion of these ingredients is the following: of concentrated nitrous acid, 2 parts 

 by weight, of water 1 part; of this mixture cooled to the temperature of the 

 atmosphere 18 oz., of Glauber's salt 14- lb. (avoirdupois), and of sal ammoniac 

 12 oz. On adding the Glauber's salt to the nitrous acid, thus diluted, the thermo- 

 meter fell from -f- 51° to — 1°, or 52 degrees; and on adding the sal ammoniac it 

 fell to — 9°, that is full 60 degrees. Nitrated volatile alkali, employed instead of 

 sal ammoniac, produced a cold rather more intense. By means of this mixture, 

 in a very few minutes, in the elaboratory before the class, I froze some spirits 

 above proof, diluted with an equal bulk of water; and another gentleman this 

 day sunk the thermometer 68°. 



On April 20, 1787, Mr. Walker effected the congelation of quicksilver by a 

 combination of these mixtures, without a particle of snow or ice. When he 

 began his experiment the temperature of the mercury was 45°; so that, the 

 freezing point of that metal being — 39°, there were produced 84*^ of cold. 

 This experiment was performed as follows. Four pans, of sizes progressively 



